Metal oxide catalyst systems for conversion of ethanol to butadiene

ABSTRACT

A process includes reacting a feed stream containing ethanol and optionally acetaldehyde in a dehydration reactor in the presence of a dehydration catalyst system having a Group 4 or Group 5 metal oxide and a support. The process includes obtaining a product stream containing butadiene from the dehydration reactor. Another process includes reacting a feed stream containing ethanol and optionally acetaldehyde in a dehydration reactor in the presence of a dehydration catalyst system containing a tungsten oxide supported on a zeolite or a tantalum oxide supported on a zeolite. The process includes obtaining a product stream containing butadiene from the dehydration reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

FIELD

Embodiments of the present disclosure generally relate to conversion ofethanol to butadiene. More particularly, embodiments of the presentdisclosure relate to the use of supported metal oxide catalyst systemsfor conversion of ethanol to butadiene.

BACKGROUND

Traditionally, 1,3-butadiene is manufactured primarily as a co-productof steam cracking to produce ethylene in the United States, WesternEurope, and Japan. In certain parts of the world where biomass forfermentation is plentiful, 1,3-butadiene is produced from ethanol.Butadiene has also been produced by the dehydrogenation of n-butane andoxydehydrogenation of n-butenes.

Bioethanol is a renewable alternative to fossil-derived gasoline. Forthe purposes of this disclosure, bioethanol is defined as ethanolmanufactured from plant materials. Various feedstocks may be used in theproduction of bioethanol, including sugars, starches and cellulosicbiomass (e.g., straw, wood, etc.). Bioethanol may be converted tobutadiene.

SUMMARY

The present disclosure provides for a process that includes reacting afeed stream containing ethanol in a dehydration reactor in the presenceof a dehydration catalyst system containing a Group 4 or Group 5 metaloxide and a support. The process includes obtaining a product streamcontaining butadiene from the dehydration reactor.

The disclosure provides for another process that includes reacting afeed stream containing ethanol and optionally acetaldehyde in adehydration reactor in the presence of a dehydration catalyst systemcontaining a tungsten oxide supported on a zeolite or a tantalum oxidesupported on a zeolite. The process includes obtaining a product streamcontaining butadiene from the dehydration reactor.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure may be understood from the following detaileddescription when read with the accompanying figures.

FIG. 1A depicts a reaction flow diagram in accordance with certainembodiments of the present disclosure.

FIG. 1B depicts a reaction flow diagram in accordance with certainembodiments of the present disclosure.

FIG. 2 depicts a reaction mechanism for the formation of butadiene fromethanol in accordance with certain embodiments of the presentdisclosure.

FIG. 3 is a line graph depicting free energy change for the formation ofbutadiene from ethanol as calculated by the HSC7 software package inaccordance with certain embodiments of the present disclosure.

FIG. 4 depicts the process scheme used in the examples provided herein.

FIG. 5 is a bar graph comparison of ethanol conversion and butadieneselectivity on various SiO₂ supported dehydration catalyst systems.

FIG. 6 is a bar graph depicting the influence of support acidity onbutadiene and ethylene selectivity.

FIG. 7 is a bar graph depicting the influence of a recycle effluent andreflux ratio on butadiene selectivity.

DETAILED DESCRIPTION

A detailed description will now be provided. The following disclosureincludes specific embodiments, versions and examples, but the disclosureis not limited to these embodiments, versions or examples, which areincluded to enable a person having ordinary skill in the art to make anduse the disclosure when the information in this application is combinedwith available information and technology.

Various terms as used herein are shown below. To the extent a term usedin a claim is not defined below, it should be given the broadestdefinition persons in the pertinent art have given that term asreflected in printed publications and issued patents. Further, unlessotherwise specified, all compounds described herein may be substitutedor unsubstituted and the listing of compounds includes derivativesthereof.

Further, various ranges and/or numerical limitations may be expresslystated below. It should be recognized that unless stated otherwise, itis intended that endpoints are to be interchangeable. Where numericalranges or limitations are expressly stated, such express ranges orlimitations should be understood to include iterative ranges orlimitations of like magnitude falling within the expressly stated rangesor limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.;greater than 0.10 includes 0.11, 0.12, 0.13, etc.).

Certain embodiments of the present disclosure relate to a process forproducing butadiene from ethanol. Conversion of ethanol, such asbioethanol, to butadiene may be performed by a one-step process (i.e.,the Lebedev process) or a two-step process (i.e., the Ostromislenskyprocess). The two-step Ostromislensky process proceeds generallyaccording to the following reaction schemes Ia and Ib:

CH₃—CH₂—OH(dehydrogenating catalyst)→CH₃CHO+H₂  (Ia)

CH₃—CH₂—OH+CH₃—CHO(dehydrating catalyst)→CH₂═CH—CH═CH₂+2H₂O  (Ib)

Reaction scheme Ia exhibits a heat of reaction ΔH=+16.51 kcal/mole, andreaction scheme Ib exhibits a heat of reaction ΔH=+7.11 kcal/mole. Asshown by reaction scheme Ia₂ below, the dehydrogenation step (Ia) may becarried out autothermally in the presence of air or oxygen (e.g., theVeba-Chemie process), with the concomitant combustion of the hydrogenformed supplying the necessary heat of dehydrogenation.

CH₃—CH₂—OH+0.5O₂→CH₃CHO+H₂O  (Ia₂)

Reaction scheme Ia₂ exhibits a heat of reaction ΔH=−43 kcal/mole(catalytic).

The one-step Lebedev process generally proceeds according to thefollowing reaction scheme II:

2CH₃—CH₂—OH→CH₂═CH—CH═CH₂+2H₂O  (II)

Reaction scheme II exhibits a heat of reaction ΔH=+23.63 kcal/mole. Thecombination of the two-step Ostromislensky process using the autothermaldehydrogenation route (Ia₂) may have a lower net heat of reaction thanthe one-step Lebedev process. Without being bound by theory, it isbelieved that butadiene produced by the one-step Lebedev process istypically less than 80% pure as compared with a typical 98% or betterpurity of butadiene produced by the two-step Ostromislensky process. Thetwo-step Ostromislensky process may exhibit a lower deactivation rate ofcatalyst. The first step of the two-step Ostromislensky process (Ia orIa₂) may exhibit a 30-50% conversion of ethanol to acetaldehyde at90-95% selectivity.

FIG. 1A is a flow diagram of two-step conversion process 5 forconversion of ethanol to butadiene using the two-step Ostromislenskyprocess, and FIG. 1B is a flow diagram of one-step conversion process 15for conversion of ethanol to butadiene using the one-step Lebedevprocess.

With reference to two-step conversion process 5 in FIG. 1A, ethanol feedstream 10 may be fed to dehydrogenation reactor 14. In certainembodiments, such as that depicted in FIG. 1A, oxygen may be fed todehydrogenation reactor 14 through oxygen feed stream 12. Oxygen feedstream 12 may include air. Although shown as separate streams, ethanolfeed stream 10 and oxygen feed stream 12 may be combined prior todehydrogenation reactor 14. Ethanol feed stream 10 may contain ethanol,including, but not limited to, bioethanol. Dehydrogenation reactor 14may contain any dehydrogenation catalyst system known to one skilled inthe art. In certain embodiments, the dehydrogenation catalyst maycontain silver. Within dehydrogenation reactor 14, at least some ethanolfrom ethanol feed stream 10 may react in the presence of thedehydrogenation catalyst system and, in certain embodiments, oxygen, toform acetaldehyde. The temperature in dehydrogenation reactor may range,in certain embodiments, from 260 to 310° C. Products fromdehydrogenation reactor 14 are discharged through dehydrogenationproduct stream 16 a. Dehydrogenation reactor product stream 16 a maycontain acetaldehyde and unreacted ethanol. Reaction of ethanol feedstream 10 in dehydrogenation reactor 14 may also form first side productstream 18 containing water.

Dehydrogenation reactor 14 may be located upstream of dehydrationreactor 22 a. In certain embodiments, dehydration reactor 22 a may be afixed bed continuous flow reactor, for example. Dehydrogenation reactorproduct stream 16 a may be fed to dehydration reactor 22 a. In someembodiments, dehydrogenation bypass stream 10 a, which is a portion ofethanol feed stream 10, may be fed to dehydration reactor 22 a. Forexample and without limitation, a portion of stream ethanol feed stream10 may be diverted as dehydration bypass stream 10 a and combined withdehydrogenation reactor product stream 16 a upstream of dehydrationreactor 22 a or fed to dehydration reactor 22 a separately fromdehydrogenation reactor product stream 16 a.

Within dehydration reactor 22 a, ethanol and acetaldehyde fromdehydrogenation reactor product stream 16 a may react in the presence ofa dehydration catalyst system including a Group 4 metal oxide, Group 5metal oxide, or tungsten oxide and a support to form dehydration productstream 24 a. Dehydration product stream 24 a may contain 1,3-butadiene.Dehydration product stream 24 a may be obtained from dehydration reactor22 a. In some embodiments, dehydration product stream 24 a is in the gasphase.

In some embodiments, two-step conversion process 5 includes recyclingdehydration recycle stream 30 a from dehydration reactor 22 a.Dehydration recycle stream 30 a may contain unreacted ethanol fromdehydration reactor 22 a. Dehydration recycle stream 30 a may containethanol, acetaldehyde, butadiene, diethyl ether, other oxygenates, orcombinations thereof. Two-step conversion process 5 may include feedingdehydration recycle stream 30 a into dehydration reactor 22 a. Forexample and without limitation, dehydration recycle stream 30 a may becombined with dehydrogenation bypass stream 10 a, dehydrogenationreactor product stream 16 a, or both. In some embodiments, dehydrationrecycle stream 30 a may be fed to dehydration reactor 22 a separatelyfrom dehydrogenation bypass stream 10 a and dehydrogenation reactorproduct stream 16 a. In some embodiments, a reflux ratio ranges from 0.5to 1.0. “Reflux ratio” as used herein refers to the ratio of the amountof dehydration recycle stream 30 a to the amount of dehydrogenationreactor product stream 16 a and optionally dehydrogenation bypass stream10 a fed to dehydration reactor 22 a, as determined by volume.

Reacting dehydrogenation reactor product stream 16 a in dehydrationreactor 22 a in the presence of the dehydration catalyst system may formsecond side product stream 26 a containing H₂ and a third side productstream 28 a containing water. In some embodiments, third side productstream 28 a is in the liquid phase. While second side product steam 26 aand dehydration product stream 24 a are shown as exiting dehydrationreactor 22 a separately, the contents of second side product steam 26 aand dehydration product stream 24 a may exit dehydration reactor 22 a asa single gaseous effluent stream and may be separated downstream ofdehydration reactor 22 a.

With reference to FIG. 1B, reaction in dehydration reactor 22 b mayoccur in substantially the same manner as in dehydration reactor 22 a asdiscussed herein, with the following differences. Reaction indehydration reactor 22 b differs from reaction in dehydration reactor 22a in that dehydration reactor feed stream 16 b is not an effluent froman upstream dehydrogenation reactor, and contains ethanol and, in atleast some embodiments, does not contain acetaldehyde. As in dehydrationreactor 22 a, reaction in dehydration reactor 22 b may producedehydration product stream 24 b containing 1,3-butadiene; second sideproduct stream 26 b containing H₂; and third side product stream 28 bcontaining water. Also as in dehydration reactor 22 a, dehydrationrecycle stream 30 b from dehydration reactor 22 b may be obtained.Dehydration recycle stream 30 b may have the same constituents asdehydration recycle stream 30 a, and may be recycled to dehydrationreactor 22 b in the same manner as dehydration recycle stream 30 a isrecycled to dehydration reactor 22 a.

Effluent from dehydration reactor 22 a or dehydration reactor 22 b mayinclude liquid effluents, such as ethanol, acetaldehyde, butadiene,diethyl ether, ethylene, ethoxy ethane, ethoxy butane, diethoxy ethane,ethoxy butane, 2-butenal, other oxygenates, or combinations thereof,which may be present in third side product stream 28 a or 28 b, forexample. Effluent from dehydration reactor 22 a or dehydration reactor22 b may include gaseous components, such as butadiene, CO, CO₂, H₂,methane, and other C₄ and lighter components, which may be present insecond side product stream 26 a or 26 b or in dehydration product stream24 a or 24 b. In some embodiments, effluent from dehydration reactor 22a or dehydration reactor 22 b may also include gaseous components, suchas N₂, O₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₂H₂, C₆₊, C₃H₆, C₃H₈, C₄H₆, C₄H₈,C₄H₁₀, C₅H₁₀, C₅H₁₂, or combinations thereof, which may be present insecond side product stream 26 a or 26 b or in dehydration product stream24 a or 24 b.

Without being bound by theory, conversion of ethanol to butadiene maygenerally proceed according to the reaction mechanism shown in FIG. 2,by aldol condensation between two acetaldehyde molecules formed uponethanol dehydrogenation. It is believed that the aldol-addition product,3-hydroxybutanal, may yield crotonaldehyde by dehydration, which maythen further be hydrogenated and dehydrated to yield butadiene. As shownin FIG. 2, the reaction mechanism generally involves the followingprincipal steps: (1) formation of acetaldehyde from ethanol bydehydrogenation; (2) acetaldehyde aldol condensation (acetaldol or3-hydroxybutanal); (3) followed by formation of crotonaldehyde; (4)reaction of crotonaldehyde with ethanol on the surface of a metal oxidedehydration catalyst system; (5) hydrogen transfer via aMeerwein-Ponndorff type mechanism; and (6) dehydration to butadiene.Thus, ethanol acts as a source of acetaldehyde, and subsequently as asource of hydride.

The feasibility of butadiene production from ethanol, as well as afavorable operational window for this reaction, has been assessed bythermodynamic equilibrium calculations using the HSC7 software package,as shown in FIG. 3. With reference to FIG. 3, butadiene production fromethanol may be performed at temperatures of at least 148° C. (423 K) andat most 425° C. (698 K), for example.

Calculated Gibbs free energies at different temperatures are summarizedin Table 1 for the steps proposed for the aldehyde condensation route.As can be seen from Table 1, the second step, that is, the coupling oftwo acetaldehyde molecules to 3-hydroxybutanal, is unfavorable, but maybe compensated for by the subsequent condensation reaction yieldingcrotonaldehyde, which is highly exergonic. In the acetaldehydecondensation route, crotonaldehyde may either be reduced by ethanol orby hydrogen that is generated in the first step.

TABLE 1 ΔG [kJ mol⁻¹] Step Reaction 298 K 653 K 733 K 12CH₃CH₂OH→2CH₃CHO + 2H₂ — −9.2 −25.1 2 2CH₂CHO→CH₃CH(OH)CH₂CHO +10.9+53.6 +59.8 3 CH₃CH(OH)CH₂CHO→C₃H₅CHO + H2O +4.2 −87.4 −98.3 4aC₃H₅CHO + CH₃CH₂OH→C₄H₆ + CH₃CHO + H₂O +7.1 −30.5 −38.9 4b C₃H₅CHO + H₂→C₄H₆ + H₂O — −21.3 −20.9 Overall values +22.2 −73.6 −102.5 for routea^([a]) Overall values +15.1 −64.4 −84.5 for route b^([b]) ^([a])Steps1, 2, 3, and 4a. ^([b])Steps 1, 2, 3, and 4b.

In some embodiments, a temperature within dehydration reactor 22 a ordehydration reactor 22 b during reaction of dehydrogenation reactorproduct stream 16 a or dehydration reactor feed stream 16 b ranges from148 to 425° C., or 250 to 500° C., or 275 to 450° C., or 300 to 400° C.,or 300 to 350° C., or 300 to 345° C., or 300 to 425° C. In someembodiments, a temperature within dehydration reactor 22 a ordehydration reactor 22 b during reaction of dehydrogenation reactorproduct stream 16 a or dehydration reactor feed stream 16 b may be anyreaction temperature as set forth in any of the Tables provided herein,or as utilized in any of the examples described herein.

A pressure in dehydration reactor 22 a or dehydration reactor 22 bduring reaction of dehydrogenation reactor product stream 16 a ordehydration reactor feed stream 16 b may be greater than 0.1 MPa, from0.1 MPa to 0.5 MPa, from 0.1 MPa to 0.2 MPa, from 0.3 MPa to 0.6 MPa,from 0.01 MPa to 0.02 MPa, or from 0.01 to 0.6 MPa. In some embodiments,pressure in dehydration reactor 22 a or dehydration reactor 22 b is ator near atmospheric pressure. Pressure in dehydration reactor 22 a ordehydration reactor 22 b may be any pressure set forth in any of theTables provided herein or utilized in any of the examples disclosedherein.

Liquid hourly space velocity (LHSV) in dehydration reactor 22 a ordehydration reactor 22 b during reaction of dehydrogenation reactorproduct stream 16 a or dehydration reactor feed stream 16 b may rangefrom 0.1 to 0.8 hr⁻¹, 0.2 to 0.6 hr⁻¹, 0.31 to 0.49 hr⁻¹, 2 to 4 hr⁻¹,or 1 to 5 hr⁻¹. LHSV in dehydration reactor 22 a or dehydration reactor22 b may be any LHSV as set forth in any of the Tables provided hereinor utilized in any of the examples disclosed herein.

A volumetric ratio of ethanol to acetaldehyde in dehydrogenation reactorproduct stream 16 a or dehydration reactor feed stream 16 b may be from9:1 to 1:0, 5:1 to 1:1, 0.9:0.1 to 0.7:0.3, 0.8:0.2 to 0.2:0.8, or 4:1,or 1:1, or 2.5:1. The volumetric ratio of ethanol to acetaldehyde indehydration reactor 22 a or dehydration reactor 22 b may be anyvolumetric ratio as set forth in any of the Tables provided herein orutilized in any of the examples disclosed herein. In embodiments,ethanol is present in excess with respect to the amount of acetaldehyde,as determined by volume percent. Without being bound by theory, it isbelieved that the presence of excess ethanol provides larger yields ofbutadiene, which allows the reaction of crotonaldehyde with ethanol toproceed. In some embodiments, the feed stream to the dehydration reactor22 a or 22 b does not contain acetaldehyde, such that acetaldehyde isnot present in dehydrogenation reactor product stream 16 a ordehydration reactor feed stream 16 b.

Catalyst Systems

Conversion of ethanol or ethanol and acetaldehyde to form butadiene mayoccur in the presence of a dehydration catalyst system that contains aGroup 4 or Group 5 metal oxide and a support. The dehydration catalystsystem may be a heterogeneous catalyst system.

In some embodiments, the dehydration catalyst system may include asupport. In certain embodiments, the support is silica (SiO₂),including, but not limited to, fumed silica or silicagel. The silica mayhave a surface area of from 200 to 480 m²/g or 250 to 380 m²/g, forexample. The silica may have a pore size ranging from 50 to 200 Å or 60Å to 150 Å, for example. The silica may be any silica known to oneskilled in the art, such as, for example and without limitation, Aerosil380 available from Aerosil; DAVISIL® 646 and DAVISIL® 636 available fromW. R. Grace and Company; and silica available from Alfa Aesar, as setforth in the examples provided herein.

In some embodiments, the support is MgO, or a magnesia-silica support(MgO/SiO₂). A magnesia-silica support may be formed by modifying asilica support with magnesium. For example and without limitation,silica may be mixed with a source of magnesium, such as magnesiumhydroxide dissolved in water. After mixing, the mixture may be dried,calcined, and dry milled. The Mg/Si ratio within the magnesia-silicasupport may be less than 1:1, greater than 2:1, or may range from 1:1 to2:1. Without being bound by theory, it is believed that themagnesia-silica support contains both basic (magnesia) and acidic(silica) components with different dispersions and locations within thesupport. Magnesia is believed to activate the aldol condensationreaction and assist in dehydrogenation of ethanol, while silica isbelieved to catalyze dehydration.

In some embodiments, the support is a zeolite. Zeolites includesilicate-based zeolites and amorphous compounds such as faujasite,mordenite, chabazite, offretite, clinoptilolite, erionite, andsihealite, for example. Silicate-based zeolites include alternating SiO₂and MO_(x) tetrahedra, where M is an element selected from the Groups 1through 16 of the Periodic Table. The zeolite may have 4-, 6-, 8-, 10-,or 12-membered oxygen ring channels. Examples zeolites that may be usedas a support in the process include zeolite A, zeolite L, zeolite beta,X-zeolite, zeolite Y, ZSM-5, MCM-22, and MCM-41. The zeolite may besodium modified, such as Na—X-zeolite. The zeolite may be potassiummodified, such as K—X-zeolite.

In some embodiments, the zeolite is microporous, macroporous, ormesoporous. A microporous zeolite is a zeolite having pores withdiameters of less than 2 nm. A mesoporous zeolite is a zeolite havingpores with diameters of from 2 to 50 nm. A macroporous zeolite is azeolite having pores with diameters of greater than 50 or greater than75 nm. The zeolite may have a crystallite size ranging from 10 to 80 μm,for example.

Without being bound by theory, it is believed that reduced acidity ofthe support may lead to reduced activity of the dehydration catalystsystem for the aldol condensation reaction used for the formation of thecrotonaldehyde intermediate, and the subsequent condensation of theintermediate with ethanol to yield the metal complex that leads tobutadiene formation. Acidic sites are believed to enhance catalystactivity. Catalyst acidity may be increased by addition of a Lewis acid,such as Zn(II) or Zr (IV). Further, it is believed that more acidicsupports form larger amounts of by-products, such as ethene and diethylether. Increased Lewis acid strength may lead to direct dehydration ofethanol to yield ethylene and ethyl ether, while decreased acid strength(increased basicity) may lead to reduced activity for condensationreaction leading to the intermediate 3-hydroxybutanal (acetaldol).

Embodiments of the dehydration catalyst system contain a Group 4 orGroup 5 metal oxide. For example, the Group 4 metal oxide may be atitanium oxide, zirconium oxide, or hafnium oxide. The Group 5 metaloxide may be a vanadium oxide, niobium oxide, or tantalum oxide, forexample.

In some embodiments, the dehydration catalyst system includes a tungstenoxide or a tantalum oxide, which may be supported on a zeolite asdescribed herein.

In certain embodiments, the dehydration catalyst system contains only asingle metal oxide. The single metal oxide may be a Group 4 metal oxide,such as a zirconium metal oxide; a Group 5 metal oxide, such as aniobium metal oxide or a tantalum metal oxide; or tungsten oxide.Embodiments that contain only a single metal oxide do not containadditional metal oxides.

In some embodiments, the dehydration catalyst system is a bimetalliccatalyst system or a trimetallic catalyst system. As used herein, a“bimetallic catalyst system” is a dehydration catalyst system in whichthe support is modified with only two metals, and is not modified withadditional metals. As used herein, a “trimetallic catalyst system” is adehydration catalyst system in which the support is modified with onlythree metals, and is not modified with additional metals. Examples ofbimetallic and trimetallic catalyst systems include but are not limitedto oxides of: copper-zinc, cobalt-zirconium, cerium-zirconium,zirconium-zinc, and copper-zirconium-zinc. At least one of the two metaloxides in the bimetallic catalyst system may be a Group 4 metal oxide,Group 5 metal oxide, or tungsten oxide. At least one of the three metaloxides in the trimetallic catalyst system may be a Group 4 metal oxide,Group 5 metal oxide, or tungsten oxide. For example and withoutlimitation, bimetallic catalyst systems contain metal oxide including,but not limited to, niobium-rhenium oxides (NbO—ReO), cobalt-zirconiumoxides, cerium-zirconium oxides, or zirconium-zinc oxides. Trimetalliccatalyst systems contain metal oxides including, but not limited to,copper-zirconium-zinc oxides.

Some specific examples of metal oxides for use herein include, but arenot limited to, NbO—ReO, Ta₂O₅, Zr—Zn oxides, Zr/Zn/Cu oxides, andtungsten oxides. Some specific examples of metal oxide/supportcombinations for use herein include, but are not limited to: NbO—ReOsupported on silica, NbO—ReO supported on Na—X-zeolite, NbO—ReOsupported on K—X-zeolite, Ta₂O₅ supported on SiO₂, Ta₂O₅ supported onNa—X-zeolite, Zr—Zn oxides supported on silica, Zr—Zn oxides supportedon magnesia-silica, Zr/Zn/Cu oxides supported on silica, Zr/Zn/Cu oxidessupported on magnesia-silica; and tungsten oxide supported on a zeolite.

Each Group 4 metal, Group 5 metal, or tungsten may be present in thedehydration catalyst system in an amount of from about 0.1 to 2 weightpercent, or 0.5 to 1.5 weight percent, or 0.5 to 3 weight percent, or 1weight percent, or any amount provided for in the examples disclosedherein.

The dehydration catalyst system may be prepared by incipient wetnessimpregnation, also referred to as capillary impregnation or dryimpregnation, by techniques known to those skilled in the art. Forexample and without limitation, the support may be contacted with anaqueous solution of a metal source (e.g., a Group 4 or Group 5 metalsource), such as a metal salt. Specific examples of metal sources foruse herein include, but are not limited to, ammonium niobate oxalatehydrate, ammonium perrhenate, tantalum chloride salt, zirconium (IV)oxynitrate hydrate (ZrO(NO₃)₂), zinc nitrate hydrate (Zn(NO₃)₂), andcopper acetate monohydrate (Cu(OAc₂)₂).

After impregnation, the support may be dried. For example and withoutlimitation, the support may be dried in air for 12 to 72 hours, or 18 to36 hours, or 24 hours; dried at an elevated temperature for 3 to 20hours, or 10 to 15 hours, or 12 hours; or combinations thereof. Theelevated temperature may be from 80° C. to 150° C., or any dryingtemperature used in the examples disclosed herein.

After drying, the support may be calcined. Calcination may convert atleast some of the metals deposited by impregnation from metallic form tometal oxides. Calcination may occur at a temperature ranging from 300 to1050° C., 350 to 900° C., or 450 to 800° C., or 500 to 600° C., or anycalcination temperature used in the examples disclosed herein.Calcination may occur in the presence of an inert gas or air.Calcination may occur for a time ranging from 1 to 48 hours, or for anyperiod of time used in the examples as disclosed herein. In someembodiments, the support is extruded or spray dried by techniques knownto those skilled in the art. After drying and calcining, the support maybe shaped and crushed, such as through a mesh.

In some embodiments, the dehydration catalyst system is made bypreparing a slurry of a water-soluble metal salt and support (e.g.,silica) in a solvent, followed by evaporation of the solvent andcalcination of the support.

Some embodiments of the dehydration catalyst system include a binder,such as alumina. The dehydration catalyst system may also include aporosity agent, such as methyl cellulose and besan.

After a period of use within dehydration reactor 22 a or dehydrationreactor 22 b, coking of the dehydration catalyst system may occur, andthe dehydration catalyst system may be subjected to a regenerationcycle. For example and without limitation, the regeneration cycle may beperformed in-situ in dehydration reactor 22 a or dehydration reactor 22b in the presence of H₂ at an elevated temperature, such as 300 to 600°C., or 400° C. to 450° C. The regeneration cycle may optionally beperformed in the presence of H₂ and moisture.

As used herein, “selectivity of butadiene” in the conversion of ethanolto butadiene by reaction of a stream containing ethanol and acetaldehydein accordance with the second step of the Ostromislensky process isdefined according to the following equation (assuming 92% selectivity toacetaldehyde from ethanol):

${{Selectivity}\mspace{14mu} {of}\mspace{14mu} {butadiene}\mspace{20mu} \left( {{mol}\mspace{14mu} \%} \right)} = \frac{{Moles}\mspace{14mu} {of}\mspace{14mu} {butadiene}\mspace{14mu} {produced} \times 100}{\begin{matrix}{{{Moles}\mspace{14mu} {of}\mspace{14mu} {ethanol}\mspace{14mu} {consumed}} +} \\{{Moles}\mspace{14mu} {of}\mspace{14mu} {acetaldehyde}\mspace{14mu} {{consumed}/0.92}}\end{matrix}}$

In some embodiments, the conversion of ethanol to butadiene by reactionof a stream containing ethanol and acetaldehyde in accordance with thesecond step of the Ostromislensky process exhibits a selectivity ofbutadiene of from 0.04 mole percent to 80 mole percent, or from 0.5 molepercent to 60 mole percent, or from 5 mole percent to 40 mole percent,or from 10 mole percent to 30 mole percent, or from 15 mole percent to20 mole percent, or at least 80 mole percent. In some embodiments, theconversion of ethanol to butadiene by reaction of a stream containingethanol and acetaldehyde in accordance with the second step of theOstromislensky process exhibits a selectivity of butadiene equal to orgreater than any of the discrete selectivities of butadiene provided inthe Tables and Examples disclosed herein.

As used herein, “process yield of butadiene” in the conversion ofethanol to butadiene by reaction of a stream containing ethanol andacetaldehyde in accordance with the second step of the Ostromislenskyprocess is defined according to the following equation:

${{Process}\mspace{14mu} {{yield}\left( {{per} - {pass}} \right)}\mspace{14mu} {of}{\mspace{14mu} \;}{{butadiene}{\mspace{11mu} \;}\left( {{mol}\mspace{14mu} \%} \right)}} = \frac{{Moles}\mspace{14mu} {of}\mspace{14mu} {butadiene}\mspace{14mu} {produced} \times 100}{{Total}\mspace{14mu} {moles}\mspace{14mu} {of}\mspace{14mu} \left( {{ethanol} + {acetaldehyde}} \right){fed}}$

Is some embodiments, the conversion of ethanol to butadiene by reactionof a stream containing ethanol and acetaldehyde in accordance with thesecond step of the Ostromislensky process exhibits a process yield ofbutadiene of from 0.8 to 5 mole percent, or 1 to 4 mole percent, or 2 to3 mole percent. In some embodiments, the conversion of ethanol tobutadiene by reaction of a stream containing ethanol and acetaldehyde inaccordance with the second step of the Ostromislensky process exhibits aprocess yield of butadiene equal to or greater than any of the discreteprocess yield of butadiene provided in the Tables and Examples disclosedherein.

As used herein, “ethanol efficiency” in the conversion of ethanol tobutadiene by reaction of a stream containing ethanol and acetaldehyde inaccordance with the second step of the Ostromislensky process is definedaccording to the following equation:

${{Ethanol}\mspace{14mu} {efficiency}\mspace{14mu} \left( {{mol}\mspace{14mu} \%} \right)} = \frac{{Moles}\mspace{14mu} {of}\mspace{14mu} {butadiene}\mspace{14mu} {produced} \times 100}{{Moles}\mspace{14mu} {of}\mspace{14mu} {ethanol}\mspace{14mu} {consumed}}$

In some embodiments, the conversion of ethanol to butadiene by reactionof a stream containing ethanol and acetaldehyde in accordance with thesecond step of the Ostromislensky process exhibits an ethanol efficiencyof from 0.04 to 70 mole percent, or from 1 to 50 mole percent, or from 5to 40 mole percent, or from 20 to 30 mole percent. In some embodiments,the conversion of ethanol to butadiene by reaction of a streamcontaining ethanol and acetaldehyde in accordance with the second stepof the Ostromislensky process exhibits an ethanol efficiency equal to orgreater than any of the discrete ethanol efficiencies provided in theTables and Examples disclosed herein.

As used herein, “acetaldehyde efficiency” in the conversion of ethanolto butadiene by reaction of a stream containing ethanol and acetaldehydein accordance with the second step of the Ostromislensky process isdefined according to the following equation:

${{Acetaldehyde}\mspace{14mu} {efficiency}\mspace{14mu} \left( {{mol}\mspace{14mu} \%} \right)} = \frac{{Moles}\mspace{14mu} {of}\mspace{14mu} {butadiene}\mspace{14mu} {produced} \times 100}{{Moles}\mspace{14mu} {of}\mspace{14mu} {acetaldehyde}\mspace{14mu} {consumed}}$

In some embodiments, the conversion of ethanol to butadiene by reactionof a stream containing ethanol and acetaldehyde in accordance with thesecond step of the Ostromislensky process exhibits an acetaldehydeefficiency of from 0.05 mole percent to 335 mole percent, or from 0.5mole percent to 200 mole percent, or from 1 mole percent to 100 molepercent, or from 10 mole percent to 50 mole percent, or from 15 molepercent to 35 mole percent. In some embodiments, the conversion ofethanol to butadiene by reaction of a stream containing ethanol andacetaldehyde in accordance with the second step of the Ostromislenskyprocess exhibits an acetaldehyde efficiency equal to or greater than anyof the discrete acetaldehyde efficiencies provided in the Tables andExamples disclosed herein.

As used herein “ethanol conversion” refers to the weight percentage ofethanol in a feedstream that undergoes conversion to butadiene duringreaction of the feedstream, which contains ethanol and acetaldehyde, inaccordance with the second step of the Ostromislensky process. In someembodiments, the conversion of ethanol to butadiene by reaction of astream containing ethanol and acetaldehyde in accordance with the secondstep of the Ostromislensky process exhibits an ethanol conversion offrom 5 weight percent to 60 weight percent, or from 10 weight percent to50 weight percent, or from 15 weight percent to 40 weight percent, orfrom 20 weight percent to 30 weight percent, or at least 50 weightpercent. In some embodiments, the conversion of ethanol to butadiene byreaction of a stream containing ethanol and acetaldehyde in accordancewith the second step of the Ostromislensky process exhibits an ethanolconversion equal to or greater than any of the discrete ethanolconversions provided in the Tables and Examples disclosed herein.

As used herein “acetaldehyde conversion” refers to the weight percentageof acetaldehyde in a feedstream that undergoes conversion to butadieneduring reaction of the feedstream, which contains ethanol andacetaldehyde, in accordance with the second step of the Ostromislenskyprocess. In some embodiments, the conversion of ethanol to butadiene byreaction of a stream containing ethanol and acetaldehyde in accordancewith the second step of the Ostromislensky process exhibits anacetaldehyde conversion of from 15 to 95 weight percent, or from 25 to85 weight percent, or from 35 to 75 weight percent, or from 45 to 65weight percent. In some embodiments, the conversion of ethanol tobutadiene by reaction of a stream containing ethanol and acetaldehyde inaccordance with the second step of the Ostromislensky process exhibitsan acetaldehyde conversion equal to or greater than any of the discreteacetaldehyde conversions provided in the Tables and Examples disclosedherein.

EXAMPLES

The disclosure having been generally described, the following examplesshow particular embodiments of the disclosure. It is understood that theexample is given by way of illustration and is not intended to limit thespecification or the claims. All compositions percentages given in theexamples are by weight.

In the Examples provided below, various dehydration catalyst systems aretested for use in the second step of the two-step Ostromislensky processfor conversion of a stream containing ethanol and acetaldehyde tobutadiene.

Catalyst Preparation Example A—Preparation of NbO—ReO Supported onSilica

A dehydration catalyst system containing 2 weight percent Nb and 0.1weight percent Re was prepared based on a silica support having asurface area of 380 m²/g, available from Aerosil as Aerosil 380. Thesilica support was subjected to incipient wetness impregnation with a99% pure aqueous solution of ammonium niobate oxalate hydrate, and a99.9% pure aqueous solution of ammonium perrhenate, both available fromAldrich. After impregnation, the silica support was dried in air for 24hours, then dried at 120° C. for 12 hours, and then calcined at 520° C.for 3.5 hours.

Example B—Preparation of NbO—ReO Supported on Zeolite

The influence of basicity of support was tested by preparation ofdehydration catalyst systems containing 2 weight percent of Nb and 0.1weight percent of Re supported on an extrudate of Na—X-zeolite, andpreparation of dehydration catalyst systems containing 2 weight percentof Nb and 0.1 weight percent of Re supported on an extrudate ofK—X-zeolite. These dehydration catalyst systems were prepared from Nband Re salts using 1/16^(th) inch extrudates of Na—X-faujasites andK—X-faujasites by dry impregnation. The Na—X-faujasite extrudates wereprepared with: SILIPORITE® G5-XP, which is a molecular sieve having a13X crystal structure and a Si/Al atomic ratio 1/1.5, available fromCHS; CATAPAL® C1, which is an alumina binder available from SasolChemicals; and methyl cellulose and besan as a porosity agent. K-LSXzeolite (potassium modified, low silica X-zeolite) was used as thestarting zeolite for preparing the K—X-faujasite extrudate. Ammoniumniobate oxalate hydrate and ammonium perrhenate salt solution was usedto co-impregnate both Nb and Re into the zeolites of the respectivedehydration catalyst systems. After impregnation, niobium and rheniumoxides were obtained on the Na—X-faujasites and K—X-faujasites followingcalcinations at 550° C.

Example C—Preparation of Ta₂O₅ Supported on Silica or Zeolite

A tantalum oxide (Ta₂O₅/SiO₂) catalyst evaluation was performed. ATa-based dehydration catalyst system was prepared from tantalum chloridesalt and a silica support by dry impregnation. The silica support wasDAVISIL® 646 having a pore size of 150 Å, available from W. R. Grace andCompany. An additional Ta-based dehydration catalyst system was preparedfrom tantalum chloride salt and a Na—X-zeolite support by dryimpregnation. Tantalum chloride was dissolved in ethanol and thesolution was used for the impregnation of the silica and Na—X-extrudatesupports, respectively. After impregnation, the supports were dried for24 hours to remove ethanol, then the dehydration catalyst systems weredried in an oven at 150° C. for 6 hours followed by calcination at 350°C. for 1 hour, followed by a final calcination at 450° C. for 4 hours.After cooling, the dehydration catalyst systems were pressed intotablets and crushed to 40-60 mesh. Both Ta₂O₅ dehydration catalystsystems contained 2 weight percent of Ta.

Example D—Preparation of Zr/Zn Oxide Supported on Silica

Two different dehydration catalyst systems containing 1.5 weight percentZr and 0.5 weight percent Zn were prepared from Zr and Zn salts usingone of two different silica supports. The two silica supports wereDAVISIL® 636 having a pore size of 60 Å, and DAVISIL® 646 having a poresize of 150 Å, both available from W. R. Grace and Company. Thedehydration catalyst systems were prepared by wet impregnation.Zirconium (IV) oxynitrate hydrate (ZrO(NO₃)₂) and zinc nitrate hydrate(Zn(NO₃)₂) salt solutions in water were used for the co-impregnation ofthe respective silica supports. After drying for 72 hours to removeexcess water, the catalysts were dried in an oven at 80° C. for 3 hours,followed by calcinations at 500° C. for 5 hours. After cooling, thedehydration catalyst systems were pressed into tablets and crushed to40-60 mesh. An influence of the pore size of the silica support on theprocess chemistry was evaluated by using the two different pore sizes,60 Å and 150 Å. Influence of promoter composition was investigated bypreparation of a third dehydration catalyst system prepared by the samemethod using DAVISIL® 646, but containing 3 weight percent Zr and 0.5weight percent Zn.

Example E—Preparation of Zr/Zn Oxide Supported on MgO/SiO₂

A dehydration catalyst system containing an oxide of Zr—Zn supported amagnesia-silica (MgSiO₂) was prepared by adding Zr and Zn salts to themagnesia-silica support by wet impregnation. The magnesia-silica supportwas prepared by dissolving silica and 15 weight percent magnesiumhydroxide in water. The solution was mixed, dried, and then calcined at550° C. The silica included DAVISIL® 636 or DAVISIL® 646. The Zr and Znsalts used to impregnate the magnesia-silica support were salt solutionsin water, and contained zirconium (IV) oxynitrate hydrate (ZrO(NO₃)₂)and zinc nitrate hydrate (Zn(NO₃)₂). After impregnation, the support wasdried for 72 hours to remove excess water, then the catalyst was driedin an oven at 80° C. for 3 hours, followed by calcination at 500° C. for5 hours. After cooling, the dehydration catalyst system was pressed intotablets and crushed to 40-60 mesh.

Example F—Preparation of Zr/Zn/Cu Oxide Supported on SiO₂

A tri-metallic dehydration catalyst system containing an oxide ofZr/Zn/Cu was prepared. The dehydration catalyst system contained 1weight percent Zr, 1 weight percent Zn, and 1 weight percent Cu. A saltsolution in water of zirconium (IV) oxynitrate hydrate (ZrO(NO₃)₂), zincnitrate hydrate (Zn(NO₃)₂) and copper acetate monohydrate (Cu(OAc₂)₂)was used for the wet co-impregnation of the silica support. The silicawas DAVISIL® 636. After drying the support to remove excess water for 72hours, the dehydration catalyst system was dried in an oven at 80° C.for 3 hours, followed by calcination at 500° C. for 5 hours. Aftercooling, the dehydration catalyst system was pressed into tablets andcrushed to 40-60 mesh.

Example G—Varying Mg/Si Molar Ratio

Dehydration catalyst systems containing Zr/Zn or Zr/Zn/Cu oxidesupported on MgO/SiO₂ were prepared with varying Mg/Si molar ratios asfollows. MgO/SiO₂ supports were prepared at different Mg/Si molarratios, 1:1 and 2:1. The MgO/SiO₂ supports were prepared by dry mullingfor 2 hours followed by wet impregnation. For preparation of thedehydration catalyst systems, an MgO/SiO₂ having an Mg/Si molar ratio of1:1 and an MgO/SiO₂ having an Mg/Si molar ratio of 2:1 were eachimpregnated with the bimetallic oxide Zr/Zn, and each contained 1.5weight percent Zr and 0.5 weight percent Zn. Also, an MgO/SiO₂ having anMg/Si molar ratio of 1:1 and an MgO/SiO₂ having an Mg/Si molar ratio of2:1 were each impregnated with the trimetallic oxide Zr/Zn/Cu, and eachcontained 1 weight percent Zr, 1 weight percent Zn, and 1 weight percentCu.

Experimental Set-Up for Each of Examples 1-15

The experimental set-up used in each of Examples 1-15 is illustrated inFIG. 4. Dehydration reactor 40 was a fixed bed continuous upstream flowreactor having a ¼″ internal diameter (ID). Dehydration reactor 40 washeated in a four zone furnace. In each of Examples 1-15, the respectivedehydration catalyst system was loaded in a 3.5″ catalyst zone in themiddle of dehydration reactor 40, between two zones of silicium carbide(SiC, 200-450 mesh particle size, available from Aldrich).

Hydrous ethanol 42 fed to dehydration reactor 40 included 190 proofethanol (95 weight percent ethanol, 5 weight percent water), andacetaldehyde 48 fed to dehydration reactor 40 was 99.99% pureacetaldehyde available from Aldrich. Prior to being fed to dehydrationreactor 40, hydrous ethanol 42 and acetaldehyde 48 were fed to staticmixer 46 from helium pressurized feed cans using liquid mass flowcontrollers 44 a and 44 b to control flow. Acetaldehyde 48 wasmaintained at 2° C. to avoid decomposition. The hydrous ethanol 42 andacetaldehyde 48 left static mixer 46 and entered dehydration reactor 40as combined feed 47 at reaction conditions.

Effluent 52 from dehydration reactor 40 flows through effluent condenser54 and liquid separator 56 downstream of dehydration reactor 40 forseparation of liquid effluent 58 and gaseous effluent 60 fromdehydration reactor 40. After separation, liquid effluent 58 wasanalyzed in an Agilent 6290 gas chromatography system 62 using an HP waxcolumn. The carrier gas used in the Agilent 6290 gas chromatographysystem 62 was helium. A wet test meter (WTM) 64 was used to measure thegas phase flow before sending the gaseous effluent 60 either directly togas analyzer 66 or to gas bag sample 68 and subsequently to gas analyzer66. Gas analyzer 66 was an Agilent Refinery Gas Analyzer. The carriergas used in the gas analyzer 66 was helium and N₂. The butadieneobserved to be primarily present in the gaseous effluent 60, andunreacted ethanol/acetaldehyde and other oxygenates were observed to beprimarily present in the liquid effluent 58.

In each of Examples 1-15, samples of the combined feed 47 were collectedat the beginning of the respective experimental run, liquid effluent 58and off-gas samples of gaseous effluent 60 were obtained after thereaction in dehydration reactor 40 was started, and the effluent ratewas measured. Nitrogen was used as a co-feed with acetaldehyde 48 andhydrous ethanol 42, and a net gas effluent rate was calculated.

In each of Examples 1-15, liquid effluent 58 from dehydration reactor 40was analyzed for the presence of ethanol, acetaldehyde, butadiene,diethylether and other oxygenates on Agilent 6290 GC system 62 using aHP wax column. Butanol was used as an internal standard to provide foraccurate analysis of liquid effluent 58 due to the water content andshifting baseline. Gaseous effluent 60, including butadiene, ethyleneand other C₄ and lighter components, were analyzed using gas analyzer 66(Refinery Gas Analyzer (RGA) from Agilent), either using gas bag sample68 or by diverting gaseous effluent 60 to gas analyzer 66 aftermeasuring an effluent rate. Conversions of ethanol and acetaldehyde werecalculated from the analysis of the combined feed 47 using Agilent 6290GC system 62 using a HP wax column and analysis of liquid effluent 58and gaseous effluent 60.

A regeneration cycle in-situ was performed at the end of eachexperimental run with H₂ overnight at 450° C. The Nb—Re bimetallic oxidecatalysts were activated overnight at 400° C. with hydrogen in thepresence of moisture. The Zr—Zn bimetallic oxide catalysts wereactivated at 300° C. with hydrogen.

Table 2 shows the range of operating conditions used during Examples1-15. The tests were mostly carried out at atmospheric pressures, butsome tests were conducted for investigating the effect of pressure onbutadiene yields, as detailed below.

TABLE 2 Parameter Range Temperature, ° C. 300-425 Pressure, psig    2-4^(a), and 50-80^(b) LHSV, hr⁻¹ 0.3-0.5^(a), and 1-5^(b)Ethanol/acetaldehyde, volumetric ratio 9:1-1:0

In Table 2, the pressure and LHSV marked with “a” were used inconjunction, and the pressure and LHSV marked with “b” were used inconjunction.

Example 1

Experimental runs were performed utilizing the experimental set-updepicted in FIG. 4 on the following dehydration catalyst systems: anNb(2 wt. %)/Re(0.1 wt. %) catalyst supported on silica prepared inaccordance with Example A; an Nb(2 wt. %)/Re(0.1 wt. %) supported on anNa X zeolite prepared in accordance with Example B; an Nb(2 wt.%)/Re(0.1 wt. %) supported on an K X zeolite prepared in accordance withExample B; a Ta₂O₅ supported on silica prepared in accordance withExample C; a Ta₂O₅ supported on Na X zeolite prepared in accordance withExample C; a Zr/Zn (1.5 wt. %/0.5 wt. %) supported on silica (150 Å)prepared in accordance with Example D; a Zr/Zn (3.0 wt. %/0.5 wt. %)supported on silica (150 Å) prepared in accordance with Example D; and aZr/Zn/Cu (1 wt. %/1 wt. %/1 wt. %) supported on silica prepared inaccordance with Example F. The temperature, LHSV, ethanol conversion,acetaldehyde conversion, butadiene conversion, ethanol efficiency, andacetaldehyde efficiency for experimental runs are shown in Table 3.

TABLE 3 Catalyst Nb/Re on Nb/Re on Ta on Zr/Zn on Zr/Zn on Nb/Re on Na XK X Ta on Na X silica silica Zr/Zn/Cu on silica zeolite zeolite silicazeolite (1.5%/0.5%) (3%/0.5%) silica Temperature, ° C. 325 340 315 325325 400 400 400 LHSV, hr⁻¹ 0.31 0.31 0.31 0.31 0.39 0.49 0.49 0.49Ethanol 23.20 16.93 9.10 25.38 30.40 41.98 54.54 22.25 conversion, wt. %Acetaldehyde 86.44 82.84 63.12 73.26 53.69 52.09 56.17 17.04 conversion,wt. % Butadiene 0.64 0.51 0.05 19.13 5.30 28.12 34.50 54.00 Selectivity,mol. % Ethanol 0.96 0.93 0.05 45.89 7.96 37.98 42.59 65.14 efficiency,mol. % Acetaldehyde 0.52 0.39 0.06 35.66 17.32 117.72 198.27 334.79efficiency, mol. %

FIG. 5 shows butadiene selectivity (mol. %) and ethanol conversion (mol.%) for the following dehydration catalyst systems: an Nb(2 wt. %)/Re(0.1wt. %) catalyst supported on silica prepared in accordance with ExampleA; a Ta₂O₅ supported on silica prepared in accordance with Example C; aZr/Zn (1.5 wt. %/0.5 wt. %) supported on silica (150 Å) prepared inaccordance with Example D; a Zr/Zn (3.0 wt. %/0.5 wt. %) supported onsilica (150 Å) prepared in accordance with Example D; and a Zr/Zn/Cu (1wt. %/1 wt. %/1 wt. %) supported on silica prepared in accordance withExample F.

Example 2

A Nb(2 wt. %)/Re(0.1 wt. %) metal oxide catalyst supported on SiO₂prepared in accordance with Example A was evaluated for butadieneproduction utilizing the experimental set-up illustrated in FIG. 4 anddiscussed above. Experimental runs utilizing the Nb(2 wt. %)/Re(0.1 wt.%) metal oxide catalyst supported on SiO₂ were repeated at reactortemperature conditions of 300-350° C. at different space velocities.Results from the experimental runs at 350° C. and an LHSV of 0.39 hr⁻¹showed a butadiene content of 6 mole percent and ethylene content of 46mole percent in the gaseous effluent. At a reactor temperature of 315°C., the butadiene content in the gaseous effluent was 3.4 mole percentand the ethylene content was 43 mole percent. As shown in Table 3, at areactor temperature of 325° C. and an LHSV of 0.31 hr⁻¹, the butadieneselectivity was 0.64 mole percent at a 23% ethanol conversion and 86%acetaldehyde conversion. Hydrogen was observed in the gaseous effluent,which may indicate the dehydrogenation of ethanol to form acetaldehyde,and insufficient aldol condensation to form crotonaldehyde to reactfurther with ethanol. The presence of ethylene in the gaseous effluentmay indicate catalytic activity for dehydration of ethanol, which may bedue to acid active sites on the silica support. Without being bound bytheory, a reduction in the acidic active sites by use of a more basicsupport may reduce selectivity to ethylene.

Example 3

Experimental runs were conducted with a 2 weight percent Ta-oxidesupported on a silica support. The 2 weight percent Ta-oxide supportedon a silica support was prepared in accordance with Example C. Theexperimental runs were conducted utilizing the experimental set-upillustrated in FIG. 4 and discussed above. The results are presented inTable 4. The highest yields of butadiene were obtained at anethanol:acetaldehyde volumetric ratio of 0.7:0.3, a temperature of 325°C., and an LHSV of 0.4 hr⁻¹. Increase or decrease of temperature reducedthe butadiene yield relative to a temperature of 325° C.

TABLE 4 Results of catalyst evaluation of ethanol:acetaldehyde over Ta(2%) on silica (150 Å) support at different temperatures and spacevelocities and 5 psig pressure Catalyst - 2% Ta on silica (150 Å)Ethanol: Acetal- Buta- Acetal- Ethanol dehyde diene Buta- dehyde Temper-conver- conver- Selec- diene Volumetric ature, LHSV, sion, sion, tivity,Yield, ratio ° C. hr⁻¹ wt. % wt. % mol. % mol. % 0.7:0.3 325 0.4 25.3873.26 19.1 8.1 0.7:0.3 340 0.4 30.33 87.84 15.6 7.9 0.7:0.3 315 0.427.50 71.25 11.6 5.0 0.8:0.2 325 0.4 18.32 77.26 14.0 4.5 0.8:0.2 3251.36 20.72 61.01 12.5 3.6 0.9:0.1 325 0.40 23.50 31.78 6.7 7.7 0.9:0.1340 0.40 23.09 29.61 9.4 2.1

With reference to Table 4, higher conversions were observed as thetemperature was increased, but reduced butadiene selectivity was alsoobserved.

Example 4

Zr/Zn bimetallic catalysts were supported on SiO₂ of different poresizes to demonstrate the effect of support pore size on the conversionof ethanol to butadiene. The Zr/Zn bimetallic catalysts supported onSiO₂ were prepared in accordance with Example D. Experimental runsutilizing the experimental set-up depicted in FIG. 4 were performedusing Zr (1.5 wt. %)/Zn (0.5 wt. %) on silica (150 Å) at differentethanol/acetaldehyde feed compositions with volumetric ratios of ethanolto acetaldehyde ranging from 0.8:0.2 to 0.2:0.8, and temperaturesranging from 300-345° C. Table 5 shows the results. The results from theexperimental runs indicate selectivity to butadiene on the SiO₂supported Zr—Zn catalysts in the gaseous effluent at the spacevelocities and feed compositions tested. The gaseous effluent waspredominantly butadiene with some ethylene or CO or CO₂. The liquideffluent contained some oxygenates, some of which were identified asethoxy ethane, ethoxy butane, diethoxy ethane, ethoxy butane and2-butenal using GC-MS. The results indicated that the presence ofacetaldehyde increases yields of butadiene. However, excess acetaldehydeproved to be detrimental to the formation of butadiene over the Zr—Zncatalysts on silica supports. The maximum selectivity of butadiene wasobserved at a volumetric ratio of ethanol:acetaldehyde of 0.8:0.2, atemperature of 325° C., 21.7% ethanol conversion, and 52.7% acetaldehydeconversion.

TABLE 5 Results of catalyst evaluation of ethanol:acetaldehyde overZr—Zn (1.5%-0.5%) on silica (150 Å) support at 325° C. and 5 psigCatalyst - 1.5% Zr—0.5% Zn on silica (150 Å) Ethanol: Acetal- Buta-Acetal- Ethanol dehyde diene Buta- dehyde conver- conver- Selec- dieneVolumetric LHSV, sion, sion, tivity, Yield, ratio hr⁻¹ wt. % wt. % mol.% mol. % 0.8:0.2 0.4 13.2 71.0 11.3 3.0 0.6:0.4 0.4 31.3 70.5 7.1 3.60.5:0.5 0.4 35.2 62.0 5.5 2.8 0.4:0.6 0.4 42.3 55.2 5.4 2.8 0.8:0.2 0.421.7 52.7 13.8 4 0.4:0.1 0.38 29.7 55.0 12.8 4.6 1.5:0.3 0.42 10.5 42.411.8 2.1 2.0:0.5 0.45 12.9 42.7 4.3 0.85

The results demonstrate that Zr—Zn supported on silica yields butadienein the gaseous effluent. Without being bound by theory, the formation ofcrotonaldehyde or 2-butenal is believed to be the intermediate step inthe reaction process. The acidity of the support of the catalyst systemis believed to affect the steps in the reaction mechanism. An increasein acidity of the support is believed to yield direct dehydration of theethanol to ethylene and formation of other oxygenate molecules, such asdiethyl ether. Without being bound by theory, the presence of excessethanol by volume in comparison to acetaldehyde is believed to providelarger yields of butadiene to allow the reaction of crotonaldehyde withethanol to proceed. A decrease in acidity of the support is believed tolead to a reduced activity of the catalyst system for the aldolcondensation reaction required for the formation of the crotonaldehydeintermediate and the subsequent condensation of the intermediate withethanol to yield the metal complex that leads to butadiene formation.

Example 5

Zr/Zn bimetallic catalysts supported on SiO₂ (60 Å) were prepared inaccordance with Example D. The series of experimental runs utilizing theexperimental set-up shown in FIG. 4 and using the Zr—Zn (1.5%-0.5%) onsilica (60 Å) catalyst resulted in a highest butadiene selectivity of 28wt % at a 9% conversion of ethanol, a temperature of 325° C., an LHSV of0.4 hr⁻¹, and an ethanol-acetaldehyde volumetric ratio of 4:1. Ethanolefficiency was calculated at 78%. Butadiene selectivity was reduced to15% with an increased ethanol conversion of 28% at a temperature of 340°C. Increasing the space velocity at a constant temperature also gavehigher ethanol conversion at lower butadiene selectivity. The influenceof the silica pore size on the butadiene selectivity, as demonstrated bycomparing the results obtained using the Zr/Zn bimetallic catalystssupported on SiO₂ (150 Å) with the results obtained using the Zr/Znbimetallic catalysts supported on SiO₂ (60 Å), indicates differences onthe catalyst surface with smaller pore size.

Example 6

The influence of metal content was evaluated by the preparation of a Zr(3 wt. %)/Zn (0.5 wt. %) catalyst supported on silica (60 Å) inaccordance with Example D. A series of experimental runs utilizing theexperimental set-up shown in FIG. 4 and using the Zr (1.5 wt. %)/Zn (0.5wt. %) on silica (60 Å) support as the catalyst system resulted in ahighest butadiene selectivity of 28% at a 42% conversion of ethanol, atemperature of 400° C., an LHSV of 0.48 hr⁻¹, and anethanol-acetaldehyde volumetric ratio of 4:1. The butadiene selectivitywas reduced to 24% with ethanol conversion of 37% at 400° C. and with a50:50 volumetric mix of ethanol and acetaldehyde. Increasing the spacevelocity to 1.9 hr⁻¹ at a constant temperature of 400° C. resulted in anethanol conversion of 41% at a butadiene selectivity of 21%. An increasein hydrogen and ethylene production was observed in the gaseous effluentat a temperature of 400° C. compared to the hydrogen and ethyleneproduction observed in the gaseous effluent at a temperature of 325° C.The butadiene composition of the gaseous effluent decreased from greaterthan 80 weight % at a temperature of 325° C. to about 45 weight % at atemperature of 400° C., but the accompanied increased production rate ofbutadiene led to an overall increase in butadiene selectivity of thefeed converted.

Experimental runs using the Zr (3 wt. %)/Zn (0.5 wt. %) catalystsupported on silica (60 Å pore size) resulted in a highest butadieneselectivity of 41% at 25% conversion of ethanol, a temperature of 400°C., an LHSV of 0.52 hr⁻¹, and an ethanol-acetaldehyde volumetric ratioof 4:1. The butadiene selectivity was reduced to 37% with an ethanolconversion of 35% at a temperature of 400° C., and an LHSV of 0.5 hr⁻¹.The butadiene selectivity was reduced to 35% at 55% ethanol conversion,a temperature of 400° C., and an LHSV of 0.48 hr⁻¹.

While not being bound by theory, it is believed that ZnO iscatalytically active for the dehydrogenation of ethanol. The silicasupport and/or a combination of the Lewis acidic metal centers maycatalyze the subsequent aldol condensation of ethanol and acetaldehyde.ZrO₂ may catalyze the Meerwein-Ponndorf-Verley reduction of acetaldol.The ethylene concentration in the gaseous effluent was increased for theZr (3 wt. %)/Zn (0.5 wt. %) catalyst supported on silica (60 Å poresize) in comparison to that obtained using the Zr (1.5 wt. %)/Zn (0.5wt. %) supported on silica under the same conditions. While not beingbound by theory, the increase in ethylene concentration in the gaseouseffluent may be due to the increase in Lewis acidity of the catalyst,which may favor side products.

Example 7

Experimental runs utilizing the experimental set-up shown in FIG. 4 andusing the Zr (1 wt. %)/Zn (1 wt. %)/Cu (1 wt. %) supported on DAVISIL®636 (60 Å) prepared in accordance with Example F were conducted. Anexperimental run in which the temperature was 400° C., the LHSV was 0.48hr⁻¹, and the feed did not contain any acetaldehyde yielded a butadieneselectivity of 59% at a 21% ethanol conversion. With a 4:1 volumetricratio of ethanol to acetaldehyde in the feed, a temperature of 400° C.,and an LHSV of 0.48 hr⁻¹, a butadiene selectivity of 54% was obtained ata 22% ethanol conversion and 17% acetaldehyde conversion. A maximumbutadiene selectivity of 75% was observed at 11% ethanol conversion, 14%acetaldehyde conversion, a temperature of 400° C., an LHSV of 0.5 hr⁻¹,and a 4:1 ethanol to acetaldehyde volumetric ratio in feed.

Addition of acetaldehyde to the feed did not provide higher butadieneselectivity with Zr (1 wt. %)/Zn (1 wt. %)/Cu (1 wt. %) supported onDAVISIL® 636 (60 Å). While not being bound by theory, this may be due tothe fact that the Cu/Zr/Zn silica supported catalyst producesacetaldehyde with pure ethanol.

Without being bound by theory, it is believed that the degree of acidityin the support affects reaction steps that are acid catalyzed. It isbelieved that more acidic supports form larger amounts of theby-products ethene and diethyl ether. Both Zn(II) and Zr(IV) are Lewisacidic and may enhance this catalyst activity. Thermal programmeddesorption (TPD) evaluations of the Cu/Zr/Zn silica supported catalystsmay be used to generate data on the acidic-basic nature of the catalystsystems.

Example 8

Experimental runs utilizing the experimental set-up shown in FIG. 4 wereperformed using the bimetallic Zr/Zn (1.5 wt. %/0.5 wt. %) on silica (60Å) prepared in accordance with Example D and the trimetallic Zr/Zn/Cu (1wt %/1 wt %/1 wt %) on silica (60 Å) prepared in accordance with ExampleF, and results for each are shown in Tables 6 and 7, respectively.

TABLE 6 Results of catalyst evaluation of ethanol:acetaldehyde overZr—Zn (1.5%-0.5%) on silica (60 Å) support at 400° C. Day 1 Day 2Catalyst - Zr/Zn on silica Time = Time = Time = Time Time = Time = Time= Time (1.5%/0.5%) 60 min. 120 min. 180 min. Average 60 min. 120 min.180 min. Average Temperature, ° C. 400 400 400 400 400 400 400 400 LHSV,hr⁻¹ 0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48 Ethanlol:Acetaldehyde 4 4 44 4 4 4 4 volumetric ratio Ethanol conversion, wt. % 49.55 17.42 31.7232.90 34.91 45.34 39.15 39.80 Acetaldehyde conversion, wt. % 60.24 43.5251.96 51.91 65.62 52.34 43.02 53.66 Butadiene selectivity, mol. % 34.2676.67 40.68 50.54 37.65 35.61 40.54 37.93 Ethanol efficiency, mol. %47.40 137.15 62.92 82.49 60.90 49.30 53.70 54.63 Acetaldehydeefficiency, mol. % 134.39 188.98 125.08 149.49 107.19 139.43 179.75142.12

TABLE 7 Results of catalyst evaluation of ethanol:acetaldehyde overZr—Zn—Cu (1%-1%-1%) on silica (60 Å) support at 400° C. Day 1, Day 1,Day 1, Day 2, Day 2, Day 2, Day 2, Catalyst - Zr/Zn/Cu on silica Time =Time = Time Time = Time = Time Time (1%/1%/1%) 60 min. 180 min. Average60 min. 120 min. 180 min. Average Temperature, ° C. 400 400 400 400 400400 400 LHSV, hr⁻¹ 0.48 0.48 0.48 0.5 0.5 0.5 0.5 Ethanlol:Acetaldehyde4 4 4 4 4 4 4 volumetric ratio Ethanol conversion, wt. % 31.52 21.3526.43 25.27 26.56 26.77 26.20 Acetaldehyde conversion, wt. % 30.52 19.5125.02 40.69 −85.39 −192.15 −78.95 Butadiene selectivity, mol. % 17.5626.29 21.93 30.36 78.65 25.96 44.99 Ethanol efficiency, mol. % 23.0134.12 28.56 46.03 45.10 13.66 34.93 Acetaldehyde efficiency, mol. %80.68 124.57 102.62 96.97 −114.91 −31.33 −16.42

As is evident from Tables 6 and 7, catalyst activity degraded over time.Without being bound by theory, the degradation of catalyst activity overtime may be related to deactivation of the catalyst or coke formation,which may block pores of the catalyst. The trimetallic Zr/Zn/Cu (1 wt%/1 wt %/1 wt %) on silica (60 Å) required higher space velocities toapproach similar butadiene yields observed for the bimetallic Zr/Zn (1.5wt. %/0.5 wt. %) on silica (60 Å). Higher acetaldehyde production wasobserved for the trimetallic Zr/Zn/Cu (1 wt %/1 wt %/1 wt %) on silica(60 Å) than for the bimetallic Zr/Zn (1.5 wt. %/0.5 wt. %) on silica (60Å). Without being bound by theory, the higher acetaldehyde productionmay contribute to the dehydrogenation of ethanol, and may allow a feedcontaining no acetaldehyde to be utilized in the presence of thetrimetallic Zr/Zn/Cu (1 wt %/1 wt %/1 wt %) on silica (60 Å) forproduction of butadiene.

Example 9

Nb/Re supported on an Na-exchanged X-type Faujasite zeolite prepared inaccordance with Example B was evaluated to determine if an increase inbasicity of support may reduce direct dehydration of ethanol to ethyleneand increase butadiene yield relative to the results observed with theNb/Re supported on silica (Example 1). Experimental runs utilizing theexperimental set-up shown in FIG. 4 were conducted using the Nb/Resupported on an Na-exchanged X-type Faujasite zeolite. The results at anLHSV 0.31 hr⁻¹ and a temperature of 325° C. yielded gaseous effluentwith 48 mol. % 1,3-butadiene. The ethylene concentration was 19 mol. %of the gaseous effluent, indicating that direct dehydration of ethanolwas occurring. At a temperature of 300° C., the gaseous effluentcontained 7 mol. % ethylene and 34 mol. % butadiene. The amount ofhydrogen present in the gaseous effluent was observed to increase overtime, indicating dehydrogenation activity of the catalyst andinsufficient aldol condensation to form crotonaldehyde to react furtherwith ethanol. Ethylene was observed in the gaseous effluent, indicatingcatalytic activity for dehydration of ethanol. Table 8 shows the resultsfor the various conditions tested in the experimental runs performed onthe Nb/Re supported on an Na-exchanged X-type Faujasite zeolite.

TABLE 8 Comparative efficiencies using Nb/Re on Na—X zeoliteTemperature, ° 325 340 315 300 325 300 340 315 LHSV, hr⁻¹ 0.31 0.31 0.310.31 0.49 0.49 0.49 0.49 Gaseous 2.42 2.14 1.49 0.99 1.18 1.29 1.74 0.95effluent flow rate, l/hr Ethanol 46.30 38.18 36.88 30.78 27.10 17.5635.10 22.35 conversion, wt. % Acetaldehyde 59.32 50.22 54.80 54.49 32.1230.09 36.04 37.55 conversion, wt. % Butadiene 4.45 5.42 3.00 2.65 3.652.86 3.06 2.44 process yield, mol. % Butadiene 8.79 12.87 7.10 14.1412.61 13.54 8.48 9.12 selectivity, mol. % Ethanol 12.60 18.60 10.6711.30 17.66 31.39 11.43 14.31 efficiency, mol. % Acetaldehyde 31.6045.44 23.08 20.51 47.88 40.10 35.76 27.37 efficiency, mol. %

Example 10

Experimental runs were performed utilizing the experimental set-up shownin FIG. 4, and using a 2% Ta supported on Na—X-zeolite prepared inaccordance with Example C. A butadiene selectivity of 5.5 mol. % at a 30wt. % conversion of ethanol was obtained using a temperature of 325° C.and an LHSV of 0.38 hr⁻¹. This result compared unfavorably to theresults obtained utilizing the same reaction conditions, but with 2% Tasupported on a silica support as the catalyst system. Utilization of 2%Ta supported on a silica support as the catalyst system resulted in a 19mol. % butadiene selectivity at a 26 wt. % conversion of ethanol. Anexperimental run performed utilizing the 2% Ta supported on Na—X-zeoliteprepared in accordance with Example C, a temperature of 340° C., and anLHSV of 0.38 hr⁻¹ resulted in a butadiene selectivity of 4 mol. %.

Example 11

Experimental runs were performed on Zr (1.5 wt %)/Zn (0.5 wt %) catalystsupported on Na—X-zeolite. The butadiene selectivity observed at atemperature of 325° C. and an LHSV 0.4 hr⁻¹ was 2 mol. % at 20 wt. %ethanol conversion. Under the same reaction conditions, using a Zr (1.5wt %)/Zn (0.5 wt %) catalyst supported on a silica support (DAVISIL®646), a butadiene selectivity of 14 mol. % at a 22 wt. % ethanolconversion was observed.

Without being bound by theory, it is believed basicity of the catalystinfluences the butadiene selectivity. It has been hypothesized thatusing a basic Na-exchanged zeolite as a support in place of a silicasupport would influence the butadiene selectivity. The directdehydration of ethanol to ethylene is prevalent with the presence ofacidic sites on the catalyst surface. The Na-exchange leaves behind someresidual acidic sites. This residual acidity of the zeolite support maycontribute to the observed increased selectivity to ethylene and carbondioxide using Zr (1.5 wt %)/Zn (0.5 wt %) catalyst supported onNa—X-zeolite, leading to decreased butadiene selectivity. The resultsdemonstrate that the use of basic zeolites as a support did not provideenhancement in butadiene yield in comparison to the use of silica as asupport.

Example 12

MgO/SiO₂ supports were used to study the increased basicity of thesupport. Experimental runs were performed with an MgO (15 wt. %)promoted DAVISIL® 646 silica supported catalyst containing Zr (1.5 wt.%)/Zn (0.5 wt. %) utilizing the experimental set-up depicted in FIG. 4.The Zr (1.5 wt. %)/Zn (0.5 wt. %) supported on MgO (15 wt. %) promotedDAVISIL® 646 silica was prepared in accordance with Example E. At atemperature of 400° C., a butadiene selectivity of 17 mol. % at 25 wt. %a conversion of ethanol was observed, with a 9 mol. % overall butadieneyield. Experimental runs were performed with an MgO (15 wt. %) promotedDAVISIL® 636 silica (60 Å) supported catalyst containing Zr (1.5 wt.%)/Zn (0.5 wt. %) prepared in accordance with Example E. Use of the MgO(15 wt. %) promoted DAVISIL® 636 silica (60 Å) supported catalystcontaining Zr (1.5 wt. %)/Zn (0.5 wt. %) resulted in a butadieneselectivity of 19 mol. % at a 40 wt. % ethanol conversion and atemperature of 400° C., with a 9 mol. % overall butadiene yield.

Example 13

In order to elucidate the influence of basicity of the support on theconversion of ethanol to butadiene, experimental runs were conductedutilizing the experimental set-up shown in FIG. 4 to compare thecatalytic activity of SiO₂, MgO, and MgO/SiO₂ supports. The ethyleneselectivity (mol. %) and butadiene selectivity (mol. %) observed usingundoped silica, magnesia-silica, and magnesia supports are shown in FIG.6. Silica gel was used as the undoped silica. The formation of certainamounts of ethylene and acetaldehyde, as main byproducts, was observedon bare silica gel. Without being bound by theory, silica gel is notperfectly pure, consequently minor amounts of impurities or isolatedsilanols may introduce some acidity to silica gel. Thus, silica supportsmay be, at least to some extent, responsible for the formation of someintermediates during the conversion of ethanol to butadiene, as well asfor the formation of ethylene, a major by-product of the ethanol tobutadiene conversion.

The binary magnesia-silica support was prepared to contain both basic(magnesia) and acidic (silica) components with different dispersions andlocations within the support. Without being bound by theory, magnesia isbelieved to activate the aldol condensation reaction and assistdehydrogenation of ethanol, while silica is believed to catalyzedehydration.

As seen in FIG. 6, the silica support exhibited greater selectivity toethylene than to butadiene. The magnesia support exhibited lowerethylene selectivity than either the silica support or themagnesia-silica support. The magnesia-silica support had a Mg/Si molarratio of 2:1, and exhibited increased butadiene selectivity comparedwith the magnesia support and the silica support.

Example 14

Experimental runs utilizing the experimental set-up shown in FIG. 4 wereperformed utilizing Nb—Re (2%-0.1%) supported on Na—X zeolite and Nb—Re(2%-0.1%) supported on K—X zeolite at a pressure of 50 psig. The Nb—Re(2%-0.1%) supported on Na—X zeolite and Nb—Re (2%-0.1%) supported on K—Xzeolite were prepared in accordance with Example B. The results from theexperimental runs are shown in Table 8.

TABLE 9 Results of catalyst evaluation at elevated pressures for ethanolto butadiene Ethanol Acetaldehyde Butadiene Pressure, Temperature,Ethanol:acetaldehyde LHSV, conversion, conversion, selectivity, Catalystpsig ° C. volumetric ratio hr⁻¹ wt. % wt. % wt. % 2% Nb—0.1% 80 3250.2:0.1 3.34 32.78 67.32 0.07 Re on Na X 50 325 0.2:0.1 5.14 74.86 79.411.56 50 350 0.2:0.1 3.52 33.36 72.37 2.45 50 325 0.2:0.1 3.45 28.9174.61 0.04 2% Nb—0.1% 50 325 0.2:0.1 1.54 23.97 86.57 0.28 Re on K X 50300 0.2:0.1 1.58 17.63 82.99 0.17 50 300 0.9:0.1 1.59 9.20 63.17 0.02

The liquid effluent produced in the experimental runs of Example 14contained a large number of components, some of which have beenidentified as low molecular weight oxygenates. The gaseous effluentcontained methane, hydrogen, CO₂ and CO. Without being bound by theory,hydration of ethanol may yield methane and hydrogen.

The results indicate that no appreciable increase in yield of butadienewas obtained with the increased basicity of the catalyst supported onNa—X zeolite, as opposed to K—X zeolite.

Example 15

Experimental runs were conducted utilizing the experimental set-updepicted in FIG. 4 to observe the influence of recycling of the liquideffluent to the dehydration reactor as a co-feed, as shown in FIG. 1A.Modifications were made to the reactor system shown in FIG. 4 to allowthe testing of the recycle concept shown in the process flow diagram inFIG. 1A by allowing the liquid effluent to be recycled back to thereactor inlet at a set flow rate. The feed and effluent compositionswere analyzed to determine the conversion of ethanol and the selectivityof butadiene. The dehydration catalyst system used in this evaluationwas a Zr/Zn/Cu (1%/1%/1%) supported on silica (60 Å) prepared inaccordance with Example F.

The reflux ratio is the volumetric ratio of recycle effluent to freshfeed that was fed to the dehydration reactor. The reflux ratio wasvaried at different space velocities at a temperature of 400° C. Thefresh feed, which had an ethanol to acetaldehyde volumetric ratio of4:1, was maintained at the start of the experiment and, afterestablishing a baseline, the amount of fresh feed was reduced as therecycle effluent from the liquid separator was introduced to the staticmixer along with the reduced fresh feed. The results, shown in FIG. 7,demonstrate that the butadiene selectivity was maintained or increasedand the ethanol conversion was decreased with a reflux ratio of 0.5 and1.0 (by volume).

Depending on the context, all references herein to the “disclosure” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present disclosure, which areincluded to enable a person of ordinary skill in the art to make and usethe disclosures when the information in this patent is combined withavailable information and technology, the disclosures are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the disclosure may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

1. A process comprising: reacting a feed stream comprising ethanol in adehydration reactor in the presence of a dehydration catalyst systemcomprising a Group 4 metal oxide and a support; and obtaining a productstream comprising butadiene from the dehydration reactor.
 2. The processof claim 1, wherein the feed stream further comprises acetaldehyde. 3.The process of claim 1, wherein the dehydration catalyst system containsonly a single metal oxide, wherein the single metal oxide comprises aGroup 4 metal oxide.
 4. The process of claim 3, wherein the dehydrationcatalyst system contains a Group 4 metal oxide that comprises azirconium metal oxide.
 5. (canceled)
 6. The process of claim 1, whereinthe dehydration catalyst system comprises a bimetallic catalyst systemcontaining only two metal oxides, and wherein at least one of the twometal oxides comprises a Group 4 metal oxide or a Group 5 metal oxide.7. The process of claim 1, wherein the dehydration catalyst systemcomprises a trimetallic catalyst system containing only three metaloxides, and wherein at least one of the three metal oxides comprises aGroup 4 metal oxide or a Group 5 metal oxide.
 8. The process of claim 1,the dehydration catalyst system comprises a cobalt-zirconium oxide, acerium-zirconium oxide, a zirconium-zinc oxide, or acopper-zirconium-zinc oxide.
 9. The process of claim 1, wherein thedehydration catalyst system comprises Zr/Zn oxides, or Zr/Zn/Cu oxides.10. The process of claim 1, wherein the dehydration catalyst systemcomprises Zr—Zn oxides supported on silica, Zr—Zn oxides supported onmagnesia-silica, Zr/Zn/Cu oxides supported on silica, or Zr/Zn/Cu oxidessupported on magnesia-silica.
 11. The process of claim 1, wherein thesupport comprises SiO₂.
 12. The process of claim 1, wherein the supportcomprises MgO/SiO₂.
 13. The process of claim 1, wherein the supportcomprises a zeolite.
 14. The process of claim 13, wherein the zeolitecomprises an Na—X-zeolite or a K—X-zeolite.
 15. The process of claim 1,further comprising, prior to reacting the feed stream comprising ethanolin the dehydration reactor, dehydrogenating a stream comprising ethanolin a dehydrogenation reactor located upstream of the dehydration reactorto form the feed stream, wherein the feed stream comprises ethanol andacetaldehyde.
 16. The process of claim 1, further comprising: obtaininga recycle stream containing unreacted ethanol from the dehydrationreactor; and feeding the recycle stream into the dehydration reactorwith the feed stream.
 17. The process of claim 16, wherein the a refluxratio ranges from 0.5 to 1.0, wherein the reflux ratio is a ratio of theamount of the recycle stream to the amount of the feed stream fed to thedehydration reactor, as determined by volume.
 18. The process of claim1, wherein the ethanol comprises bioethanol.
 19. The process of claim 1,wherein a temperature in the dehydration reactor during reaction of thefeed stream ranges from 148 to 500° C.
 20. The process of claim 1,wherein a pressure in the dehydration reactor during reaction of thefeed stream is from 0.01 to 0.6 MPa.
 21. The process of claim 1, whereina liquid hourly space velocity in the dehydration reactor duringreaction of the feed stream is from 0.1 to 5 hr⁻¹.
 22. The process ofclaim 1, wherein the feed stream does not contain acetaldehyde.
 23. Theprocess of claim 1, wherein the feed stream comprises ethanol andacetaldehyde, and wherein a volumetric ratio of ethanol to acetaldehydein the feed stream ranges from 9:1 to 1:1.
 24. A process comprising:reacting a feed stream comprising ethanol and optionally acetaldehyde ina dehydration reactor in the presence of a dehydration catalyst systemcomprising a tantalum oxide supported on a zeolite; and obtaining aproduct stream comprising butadiene from the dehydration reactor.25.-26. (canceled)